The broad and long range objective of the proposed research is to understand the extent to which adaptive response of enzymes in a metabolic pathway is related to pathway position, and the extent to which evidence for natural selection at individual loci can be coupled to simple responses in selection on life-history associated metabolic energy storage pools. Using Drosophila as a model system we will identify those pathway steps involved in glycolysis and the Krebs cycle which are responding to natural selection and thereby, in theory, identify those steps that possess the potential to modulate flux through glycolysis and its branch points. Specifically this will involve collection of population data on Drosophila melanogaster, D. simulans and a single sequence for D. Yakuba, for DNA sequence variation at eight genes involved in the glycolytic and Krebs cycle. A second aim will determine if the amino acid polymorphism uncovered in the active site of triose phosphate isomerase in Drosophila melanogaster affects the in vitro function of the enzyme. A third aim is to determine the extent to which amino acid polymorphisms and divergence at four enzymes will be connected with known 3D structures and domains of established functional significance. Fourth, the extent to which latitudinal clines exist for metabolic pools and amino acid polymorphisms at pathway points will be examined in North America. Finally, the potential of individual pathway steps, when depressed in activity, to modulate flux and hence affect metabolic pool levels will be assessed.